1. Field of the Invention
The present invention relates to wafer processing and more particularly to a method and apparatus for ultra thin wafer backside processing.
2. Description of Related Art
Several factors are driving the trend toward thinner chips having dimensions of less than 4 mils. Such ultra thin chips generally result in lower substrate resistance, allow for the stacking of chips to meet package thickness requirements, and avoid costly thick epitaxial layers in high voltage applications.
Conventionally, a temporary support substrate or carrier can be adhered, usually through an adhesive layer, to the front side of a device wafer to facilitate wafer back grinding and a subsequent thin wafer handling and back side processing. The carrier can be dummy silicon wafer, glass wafer, polymer or polymer based composite substrate, or thick tape. A rigid carrier helps to reduce wafer warping and prevents wafer breakage during handling and processing. However, removal of the carrier usually involves complex operations and thus leads to low throughput as well as the risk of wafer breakage.
In another approach, a rigid edge ring can be formed on the periphery of a thin wafer to facilitate thin wafer handling and processing. The ring can be obtained by etching or mechanically back grinding a wafer while leaving an edge on the wafer periphery intact, or by adhering an extra ring on the periphery of a thin wafer. However, this approach suffers the disadvantage of having a low throughput during wafer thinning and/or edge ring removal, as well as having a reduced active area (due to the wafer area devoted to the circumference).
There is therefore a need in the art for a method and apparatus for ultra thin wafer backside processing that overcomes the disadvantages of the prior art. The method and apparatus preferably provide for improved throughput with low risk of wafer breakage. The method and apparatus also preferably provide for wafers of 4 to 2 mils thickness and less at a low cost. The method and apparatus further preferably provide for a high wafer area usage.